Group transmissions having one multi-speed main transmission and one splitter group front-mounted thereon by transmission technology, the same as one range change group rear-mounted by transmission technology on the main transmission, have been known for a long time and used preferably in industrial vehicles. By a splitter group, generally designed with two speeds, having one ratio change corresponding to approximately one half of a central ratio change between two consecutive ratio stages of the main transmission. The ratio changes of the main transmission are halved and the number of gears of the group transmission available is doubled. By a usually two-speed range change group with one ratio change covering the whole speed ratio change of the main transmission approximately by a medium ratio jump between two consecutive ratio stages of the main transmission, the range of the whole transmission is about doubled and the number of gears of the group transmission available is again doubled. Relative to a three-speed main transmission (having three forward gears and one reverse gear), this results in a 12-gear group transmission with a total of twelve forward gears and a maximum of four reverse gears and relative to a four-speed main transmission having four forward gears and one reverse gear, a 16-gear group transmission with a total of sixteen forward gears and a maximum of four reverse gears. Such a group transmission has, in comparison with a singe-unit transmission having a similar number of gears and similar gradation and range, a clearly more compact dimensions and lighter weight. But since in a group transmission many gearshifts require the change of ratio stages in many parts and thus the sequence is relatively complicated, most group transmissions known are designed either partly automated or fully automatedly shiftable.
A general view of the Applicant's automated group transmission has been published in the periodical “ATZ9/2004”, pages 772-783. From the line of products of automated shift transmissions designated as the AS-Tronic Family are the transmission of the AS-Tronic middle line of products produced for medium heavy industrial vehicles and the transmissions of the AS-Tronic line of products provided for heavy industrial vehicles respectively designed as group transmissions with one multi-speed, that is, main transmissions provided with three or four forward gears, a two-speed splitter group front-mounted on the main transmission and a two-speed range change group rear-mounted on the main transmission. The main transmission is constructed with countershaft design, provided with unsynchronized dog clutches and has, in the case of the AS-Tronic middle line of products, a single countershaft, the same as in the case of the AS-Tronic line of products, two countershafts for reasons of weight and space optimation. In both lines of products, the main transmission is optionally designed with a direct gear (iHG—min=1). The splitter group is designed as a countershaft with two shiftable high ratios (iHG—min<1). The splitter group is designed as a countershaft with two shiftable input constants for the main transmission. The range change group is designed as a two-speed, planetary transmission with one shiftable direct gear ratio (iGP=1) or a high gear ratio (iGP>>1).
A group transmission with one multi-speed main transmission having a countershaft design, one splitter group front-mounted thereon with two shiftable input constants of the main transmission and one range change group rear-mounted on the main transmission in planetary construction has moreover been disclosed in WO 1999/00612 A1. This known group transmission, when equipment with a different toothed gear pair forming an input constant of the main transmission, can optionally be designed as direct gear transmission or as high gear transmission. EP 0 769 641 B1 describes an alternative group transmission with one two-speed main transmission of countershaft construction (with two forward gear speeds and one reverse gear speed), one three-speed splitter group front-mounted thereon and one range change group rear-mounted on the main transmission in planetary construction.
The group transmissions of “the AS-Tronic” line of products and of the AS-Tronic middle line of products, have been built with synchronized shift clutches of the splitter group and of the range change group combined in a common shift set, whereas the main transmission was designed to be controlled by a dog clutch, that is, shiftable by way of unsynchronized clutches. But since the concerned synchronized separating clutches, due to a complicated construction, are comparatively expensive and require a relatively large space and, due to wear, the lifetime of the whole group transmission is limited. Future designs of such group transmission could be provided to design dog shifted, together with the main transmission and the range change group.
In such a group transmission, due to the unsynchronized design of the range change group, a special shift sequence is required which clearly differs from that of a group transmission which, to a great extent, is identical, but is provided with a synchronized range change group. An adequate method for shift actuation of a group transmission, having an unsynchronized range change group, has been suggested in DE 101 52 857 A1. In this method it is provided, in essence, that in a range shift the front-mounted group is first shifted together with the range change group to interrupt the energy flow in their neutral position, the main transmission is then decelerated by way of a transmission brake and subsequently there begins a change of the rotational speed of the prime mover to the synchronized rotational speed of the target gear. After shifting the main transmission, the front-mounted group is synchronized to its target ratio stage. When the synchronous rotational speed is reached by the prime mover, the target ratio stage of the range change group is activated.
It is, of course, disadvantageous in this known method that the presence of a front-mounted group or a splitter group front-mounted on the main transmission is assumed and that the shift sequence can only be used in a range change upshift, the same as the reaching of the synchronized rotational speed by the prime mover to be expected prior to activation of the target ratio stage is delayed.
With this background, this invention provides an improved method to overcome the problems of actuating shifts of an automated group transmission of the above mentioned kind, which is suitable for carrying out range upshifts and range downshifts which, compared to the already known method, makes a faster shift sequence possible and which can also be used in group transmission, which have no front-mounted group or no splitter group front-mounted on the main transmission.